DESCRIPTION: The overall goal of these studies is to elucidate the thalamic mechanisms underlying the perception of painful stimuli and chronic pain. These novel studies are made feasible by the unique opportunity afforded to us during functional stereotactic neurosurgery when we are able to record the activity of neurons and determine the effects of microstimulation in awake patients with movement disorders or chronic pain. The major aims of the project are to I: Demonstrate the existence of nociceptive neurons within human Vc (the ventrobasal complex; VB), characterize their responses, determine whether microstimulation at such sites gives rise to painful sensations and examine whether blocking the activity of the neurons in this region will result in alteration of pain perception II: Perform similar studies but for neurons located ventroposterior to Vc in a region termed Vcpc/VMpo. III. Perform similar studies as in I and II above but for neurons located in medial thalamus. IV: To analyze the incidence, locations and firing patterns of bursting cells (proposed to contribute to chronic pain) in medial and lateral thalamus and determine the effects of blocking their activity on chronic pain. These goals will be achieved by a combination of extracellular neurons recordings, microstimulation-evoked sensations and effects of temporary block of neuronal activity in awake patients. The proposed studies will test the hypotheses that Vc, Vcpc/VMpo, and medial thalamus are involved in mediating various aspects of the pain experience and that cells firing spontaneously in a bursting pattern may be related to chronic pain. The results of these novel and unique studies should considerably advance our understanding of the role of thalamus in both chronic and acute pain and could provide a radical new conceptual framework of thalamic pain mechanisms. Improved understanding of thalamic mechanisms of acute and chronic pain may lead to the development of new therapeutic approaches.